AP Biology Chapter 23.3-23.4

Which of the following are causes of evolutionary change?
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Terms in this set (19)
Which of the following are causes of evolutionary change?
- gene flow
- natural selection
- mutation
- genetic drift
Generation-to-generation change in the allele frequencies in a population is _____.
microevolution
The evolutionary effects of genetic drift are greatest when _____.
the population size is small
What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?
founder effect
In the beetles described in the animation, there were two alleles for color, brown and green. Suppose that you discover a very small population of these beetles, consisting of the individuals shown below. How can you calculate the frequency of each allele in this population?
1. Brown Alleles
2. 8
3. 20
4. 0.4
5. 0.6
The three major mechanisms of evolution differ in how they work, and as a result often have different effects on a population. Review your understanding of natural selection, genetic drift, and gene flow by sorting the statements below into the correct bins.
Drag each statement into the appropriate bin depending on whether it applies to natural selection, genetic drift, or gene flow.
natural selection:
- consistently causes a population to become better adapted to its environment
- cannot cause a harmful allele to become more common
- a result of differential success in reproduction

genetic drift:
- can result from the founder effect
- can result from the bottleneck effect
- causes allele frequencies to fluctuate randomly

gene flow:
- a result of the movement of fertile individuals or their gametes
- can introduce new alleles into a population's gene pool
Populations evolve for many reasons. Suppose there is a population of plants that have either purple flowers or white flowers, and the allele for purple flowers is dominant. This means that plants with two purple alleles have purple flowers. Plants with one purple allele and one white allele also have purple flowers. Only plants with two white alleles have white flowers.
For each event or condition described below, answer the following questions.
a. natural selection
b. frequency of white allele increases

c. genetic drift
d. frequency of purple allele increases

e. genetic drift
f. allele frequencies change but not predictably

g. natural selection
h. frequency of purple allele increases

i. gene flow
j. frequency of white allele increases
Which type of selection tends to increase genetic variation?
Disruptive selection
In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following?
The value of a particular characteristic; characteristics of an organism can include such traits as size and color.
True or false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population.
False
Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today?Directional selectionWomen often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies?Stabilizing selectionBlack-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers?Disruptive selectionSmall Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards?Stabilizing selectionIn evolutionary terms, an organism's fitness is measured by its _____.contribution to the gene pool of the next generationBlue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____.directional selectionWhat is the only evolutionary mechanism that consistently leads to adaptive evolution?natural selectionFor 1981, 1987, and 1990, how does the frequency of left-mouthed breeding adults compare to the frequency of left-mouthed individuals in the entire population?Most of the breeding adults had the opposite phenotype of that which was most common in the population.What do these comparisons suggest about when natural selection favored left-mouthed individuals over right-mouthed individuals?Left-mouthed individuals were selected for when right-mouthed individuals were more common, and vice versa.